Currently, a problem of electric power shortage is solved only in a minority of regions in China; a majority of regions and large cities still face a problem of shortage of electric power supply, and power supply quality still less can be guaranteed; commercial power cannot meet a requirement of an electronic device with a high requirement for power supply quality.
A UPS emerges as the times require, and a role of the UPS is to replace the commercial power to provide electric energy for a load when commercial power supply stops; the UPS is internally disposed with an energy storage apparatus, and when the commercial power is abnormal or interrupted, the UPS maintains power supply to the load with electric energy in the energy storage apparatus in an inverting conversion method, so that the load maintains normal operations.
Generally, the UPS includes the following several parts: a rectifier, an inverter, a charging circuit, a discharging circuit, and an energy storage apparatus; in an existing UPS circuit, the rectifier is also used as a discharging circuit of the energy storage apparatus, but a charging circuit is still required, which makes a circuit structure complicated; in another existing UPS circuit, the commercial power and the energy storage apparatus separately use two independent conversion circuits (a rectifier or an inverter), where a charging circuit and a discharging circuit of the energy storage apparatus share a high-power battery conversion circuit; such a type of UPS circuit needs the high-power battery conversion circuit, making a UPS circuit structure complicated, and the high-power battery conversion circuit is high in cost; in conclusion, a structure of the existing UPS circuit is complicated.